The use of rheometers and viscometers in rubber compounding and testing is extensively known. Reference herein will be made to rheometers generally, it being understood that the concept of the invention may be applied equally to both rheometers and viscometers. Rheometers typically comprise a pair of dies which mate with each other to form a cavity therebetween. An uncured rubber sample is placed within the cavity between the dies, the dies are heated to effect a cure, and one of the dies is caused to rotate or oscillate in a predetermined fashion. Such structure and technique is state-of-the-art and is presented to form a background for the invention herein.
The upper die is typically movable only in a vertical direction to make engagement with the lower die which, while not movable vertically, is connected to a motor or appropriate gearing to effectuate the desired rotational or oscillating motion. In the prior art, the lower die, often referred to as a rotor or rotating disc, is designed to allow the rubber to flow around it, making it necessary to pull the rubber from the rotor at the end of the rheometer test. In such embodiments, the rotor is actually encased by the rubber. Often, the rubber tears as it is being removed from the rotor and it becomes necessary to actually remove the rotor from the rheometer. This is not only time consuming, but also allows the upper and lower dies to cool down, delaying the testing operation and generating extra work effort.
In designs in which the rotor is not encased by the rubber, it is necessary that the rotating die be sealed with the stationary die to define a closed cavity. In the prior art, the moving die is sealed against the die holder, rather than directly against the mating die itself. Such seal is subjected to both axial and radial forces during the operation of the rheometer, causing such seal to experience rapid wear, necessitating frequent replacement. Indeed, the replacement of such seals has been found necessary on at least a daily basis, if not more frequently. Prior art seals, circumferential to the rotating disc, are difficult and time consuming to replace. Not only is the seal itself difficult to replace, but removal of the die to effectuate such replacement is also a time consuming and difficult task.